This invention relates to illuminated apparatus, particularly to a means of mounting a lens assembly therein which provides improved thermal endurance for the lens assembly as well as minimizing adverse affects of shock and vibration thereon. More particularly, this invention relates to illuminated indicator devices of the aforementioned type which are to be compatible with night vision goggle (NVG) technology and to seals which prevent the egress of light and the ingress of contaminants around the lens assembly.
Illuminated indicators are generally mounted on or contained in a panel to provide a signal by their illumination of some remote function. In certain devices the mere illumination provides the signal; in other devices a captioned lens is illuminated to provide information or instruction in addition to the illumination signal. Light leakage around a lens or from other cracks or joints of the indicator device is undesirable in many applications and is a particular problem when such indicators are to be compatible with NVG technology as in the cockpit of an aircraft. NV goggles greatly intensify light to allow the wearer to see clearly at night. The illuminated indicator devices found on an aircraft annunciator panel have lens assemblies which include filters to specifically filter out (block) certain wavelengths of the illuminated indicator light source such as the infrared and near infrared wavelengths, and to pass only the visible wavelengths. Light containing the unfiltered wavelengths leaking or escaping around the lens can produce a glare for the wearer of the night vision goggles and can also be detected by systems particularly sensitive to infrared wavelengths. This problem is magnified in illuminated indicator devices used in aircraft because high intensity light sources are used to enable the devices to be readable in bright sunlight.
Another problem particularly prevalent in aircraft cockpits is wide temperature variations, influenced primarily by the presence or absence of the sun, but also by localized affects of plural high intensity lamps contained within the device or panel.